14. Nervous System II Flashcards
What does the CNS consist of?
Brain
Spinal cord
What is the brain protected by?
Cranium
Cranial meninges
Cerebrospinal fluid (CSF)
Blood brain barrier (BBB)
What is the spinal cord protected by?
Vertebral column
Meninges
What are meninges?
Layers of connective tissue that form protective membranes
They surround and encase the brain and spinal cord within the skull and spinal column
What are the three layers of meninges that cover the brain and spinal cord?
Dura mater
Arachnoid mater
Pia mater
What is the dura mater?
“Tough mother”
Tough outer layer
Has 2 layers in the brain
What do the two layers of dura mater in the brain do?
Create venous sinuses
What do venous sinuses do?
AKA Bridging veins
Allow blood to drain out of the brain into the jugular veins
What is the arachnoid mater made up of?
Collagen and elastic fibres
What is the subdural space between the dura mater and arachnoid mater filled with?
Interstitial fluid
What is the pia mater?
Innermost layer of the meninges
Thin, transparent and highly vascular
In direct contact with the brain
Follows contours of the brain
What does the pia mater contain?
Blood vessels that supply the spinal cord
What is the subarachnoid space between the arachnoid mater and pia mater filled with?
Cerebrospinal fluid (CSF)
What is a subdural haematoma?
Venous bleed in space below the dura mater
Develops slowly
Can happen in Alzheimers disease due to brain shrinkage
What is a subarachnoid haemorrhage?
Arterial bleed in the space below the arachnoid mater
Rapid development
From Berry aneurism
Feels like a thunderclap headache
What is cerebrospinal fluid (CSF)?
Clear, colourless* liquid that protects the brain and spinal cord from mechanical and immunological injury
Nourishes the brain and spinal cord
*contains no blood cells
What does CSF consist of?
Filtered blood
Water with ions and glucose
Why is CSF colourless?
Blood cells are too large to filter through
Where can you find CSF?
Subarachnoid space
Ventricles* in brain
Central canal of spinal cord
Fourth ventricle (back of brain) used in cranio-sacral therapy
Where is CSF produced ?
Ependymal cells
How much CSF is produced a day?
500ml
How much CSF can be found in the brain?
150ml
What happens to excess CSF that can’t fill around the brain?
Gradually absorbed back into blood
What are the functions of CSF?
Supports/protects the brain and spinal cord
Shock absorber
Keeps them moist
Circulates nutrients and waste
Maintains uniform pressure around brain
Maintains optimal chemical environment for nerve signalling
Where does blood flow to the brain from?
Vertebral arteries (x2)
Carotid arteries (x2)
What percentage of the body’s oxygen and glucose does the brain use at rest?
20%
What does the blood brain barrier do?
Protects brain from toxins, harmful substances and bacteria
How does the BBB protect the brain from toxins, harmful substances and bacteria?
By maintaining tightness of capillaries
By maintaining junctions between cells
What maintains the BBB?
Astrocytes that wrap around the capillaries
What substances can transport across the BBB?
- Lipid soluble substances: alcohol,
anaesthetics - Glucose (active transport)
- Gases
- Ions
What substances can’t transport across the BBB easily?
Proteins
Some drugs
What are the four areas of the brain?
Brainstem
Diencephalon
Cerebrum
Cerebellum
What are the parts of the brainstem?
Midbrain
Pons*
Medulla oblongata
‘Bridge’
What are the parts of the diencephalon*?
interbrain
Thalamus*
Hypothalamus
Epithalamus
*80%, core of the brain
Where can you find the brainstem?
Top of the spinal cord
Continuation of the spinal cord
What does the brainstem pass through?
Foramen magnum (large hole)
Which centres are located in the medulla oblongata?
Respiratory centre
Cardiac centre
What does the medulla oblongata control?
Breathing
Cardiac output
Heart rate
Blood pressure
Vomiting reflex
Coughing reflex
Hiccupping reflex
Which cranial nerves are located in the medulla oblongata?
9-12
Which tract is located in the medulla oblongata?
Corticospinal tract (motor)
What does the pons control?
Breathing
Which cranial nerves are located in the pons?
5-8
Which tract does the pons relay?
Motor
What does the midbrain contain?
Substantia nigra
What is the substantia nigra?
Large, darkly-pigmentated area
What does the substantia nigra contain ?
Dopamine releasing neurons that control subconcious muscle activities
What does the midbrain do?
Controls eye reflexes and tracking
Controls head and neck movements
Auditory tracts
Transfers motor tracts
Which cranial nerves are located in the midbrain?
III - Oculomotor
IV - Trochlear
What is the thalamus?
Major part of the diencephelon
Relay centre of the brain
What percentage of the diencephalon is made up of the thalamus?
80%
What does the thalamus do?
Relays sensory information to the cerebrum
Integrates sensory and motor information
What does the epithalamus do?
Connects limbic system to other parts of the brain
Which gland is located in the epithalamus?
Pineal gland
Which hormone does the pineal gland secrete?
Melatonin
What does the hypothalamus do?
Regulates hormones and homeostasis Controls body temperature Regulates emotional/behavioural patterns Regulates appetite/satiety Regulates circadian rhythm
What type of information does the hypothalamus receive?
Sensory
Which nervous system does the hypothalamus control?
Autonomic nervous system
Where is the cerebellum located?
Inferior and posterior aspect of the cranium
How many neurons can be found in the cerebellum?
50 billion*
Majority are interneurons
*Half the total number found in the brain
What are the functions of the cerebellum?
- Balance/posture (propreoception)
- Co-ordinates smooth sequences of movement to ‘skilled’ levels
- Error correction during ongoing movement (learning an instrument, learning to walk)
- Cognition, thought and language processing
What can damage the cerebellum?
Chronic alcohol abuse
Coeliac’s disease
Thiamine (B1) deficiency (malnourished)
What are the symptoms of a cerebellar disease?
Ataxia* - lack of muscle co-ordination
Stumbling
Unsteadiness
Slurred speech
Intention tremor (tremor when doing a movement e.g. hand shaking when putting key in lock)
*notice wide-legged stance
What are the areas of the cerebrum called?
Left and right hemispheres
What does the cerebrum contain?
- Outer cerebral cortex with multiple foldings
- Deeper cerebral region
What is the outer cerebral cortex also known as?
Grey matter
What is the deeper cerebral region also known as?
White matter
What is grey matter made up of?
Cell bodies
Dendrites
Unmyelinated axons
What is white matter made up of?
Myelinated axons
How are the left and right hemispheres of the cerebrum connected?
By the corpus callosum
What does the corpus callosum do?
Co-ordinates movements between sides e.g. walking
What are the functions of the cerebrum?
Sensory perception
Motor control of skeletal muscles (movement)
What is the name of the descending motor tract?
Corticospinal tract
What is the corticospinal tract made up of?
Motor neuron axons
Where do the motor tracts cross over (decussate)?
In the medulla oblongata
What impact does the motor tracts decussating have on the body?
- Left side of brain co-ordinates right side of body
- Right side of brain co-ordinates left side of body
What are the four lobes of the cerebrum called?
- Frontal
- Temporal
- Parietal
- Occipital
What does the frontal lobe of the cerebrum control?
Motor skills
What does the temporal lobe of the cerebrum control?
Hearing
What does the parietal lobe of the cerebrum contain?
Sensory cortex
What does the occipital lobe of the cerebrum control?
Vision
What does the outer cerebral cortex contain?
Sensory cortex
Motor cortex
What does the sensory cortex do?
Receives sensory input (e.g. touch, vibration) and maps it out
What does the motor cortex do?
Controls voluntary movements of specific muscles
What is the limbic system?
Area of brain that is active with different emotions
What is the limbic system formed of?
Cerebrum
Diencephalon
Midbrain
What are the key structures within the limbic system?
Hypothalamus (diencephalon)
Hippocampus (cerebrum)
Amygdala (cerebrum)
When does the limbic system become active?
When dealing with emotional responses
What is the key area for emotions?
Amygdala
What does the hippocampus do?
Encode and retrieve memories
What percentage of cardiac output does the brain receive?
20%
How much blood does the brain receive?
750ml every min
What is the Circle of Willis?
Where the carotid and vertebral arterial systems meet
The Circle of Willis is a common location for which pathology?
Berry aneurysm
How many cranial nerves are there?
12 pairs
What are the cranial nerves?
- Olfactory
- Optic
- Oculomotor
- Trochlear
- Trigeminal
- Abducens
- Facial
- Vestibulocochlear
- Glossopharyngeal
- Vagus
- Accessory
- Hypoglossal
Which cranial nerves are located in the cerebrum?
I Olfactory
II Optic
Which cranial nerves are located in the midbrain?
III Oculomotor
IV Trochlear
Which cranial nerves are located in the pons?
V Trigeminal
VI Abducens
VII Facial
VIII Vestibulocochlear
Which cranial nerves are located in the medulla oblongata?
IX Glossopharyngeal
X Vagus
XI Accessory
XII Hypoglossal
Mnemonic for remembering the cranial nerves
Oh, Oh, Oh, To Touch And Feel Vintage Green Velvet, Ahh Heaven!
Cranial nerve I - name, function, location
I Olfactory
Sense of smell
Cerebrum
Unmylinated
Cranial nerve II - name, function, location
II Optic
Vision
Cerebrum
Densely mylinated, highspeed avoids double vision when turning head
Cranial nerve III - name, function, location
III Oculomotor
Eye movements, eyelid opening, pupil dilation
Midbrain
Cranial nerve IV - name, function, location
IV Trochlear
Eye movements
Midbrain
Cranial nerve V - name, function, location
V Trigeminal
Facial sensations, chewing, some taste
Pons
Cranial nerve VI - name, function, location
VI Abducens
Eye movement (abducts eye)
Pons
Cranial nerve VII - name, function, location
VII Facial
Taste, facial expressions, salivary glands
Pons
Cranial nerve VIII - name, function, location
VIII Vestibulocochlear
Hearing, balance
Pons
Cranial nerve IX - name, function, location
IX Glossopharyngeal
Taste, swallowing, tongue sensations
Medulla oblongata
Cranial nerve X - name, function, location
X Vagus
Sensory/motor functions in chest/abdomen
Medulla oblongata
Cranial nerve XI - name, function, location
Accessory
Neck and shoulder movement
Medulla oblongata
Cranial nerve XII - name, function, location
Hypoglossal
Tongue movement and speech
Medulla oblongata
How many eye muscles does the oculomotor nerve (III) move?
4 out of 6
Moves eyeball
Elevates eyelid
How many eye muscles does the trochlear nerve (IV) move?
1 out of 6
Rotation
Used in reading
How many eye muscles does the abducens nerve (VI) move?
1 out of 6
Abducts eye
What can damage to the oculomotor, trochlear or abducens nerves cause?
Strabismus (squint)
Ptosis (drooping of upper eyelid)
Diplopia (double vision)
What is strabismus?
One eye crossed
What is ptosis?
Drooping of upper eyelid
Damage to CNIII oculomotor
What is diplopia?
Double vision
What are the branches of the trigeminal nerve (V)?
Ophthalmic
Maxillary
Mandibular
What is the vagus nerve?
Largest nerve of the autonomic nervous system
What information does the vagus nerve carry?
All sensory information from chest and abdomen
(Heart, GIT, lungs)
What can damage to the vagus nerve cause?
Tachycardia
Dysphagia
Vaso-vagal syncope (fainting)
Mnemonic for remembering the cranial nerve functions
Some - Sensory Say - Sensory Money - Motor Matters - Motor But - Both My - Motor Brother - Both Says - Sensory Big - Both Brains - Both Matter - Motor More - Motor
Where does the spinal cord begin?
At the foramen magnum
Where does the spinal cord terminate?
At vertebral level L2
Where does the spinal cord meninges tissue continue to?
To level S2 (sacrum)
What is the name of the terminus of the spinal cord?
Conus
What is the cauda equina?
Spinal nerves that continue beyond the conus
What does the spinal cord consist of?
White matter around a core of grey matter
What does the spinal cord white matter consist of?
Tracts (bundles of myelinated axons)
Which tracts make up the spinal cord white matter?
Motor tracts (descending)
Sensory tracts (ascending)
Which direction does the motor tract of the spinal cord go and what does it do?
Descending
Controls voluntary and involuntary movement
(posture, balance)
Which direction do the sensory tracts of the spinal cord go and what do they do?
Ascending
Transmit impulses from skin, tendons, muscles and joints
(touch, vibration, proprioception)
What does the spinal cord grey matter consist of?
Cell bodies
Dendrites
How is the spinal cord grey matter divided up?
Posterior (dorsal) horn
Anterior (ventral) horn
What does the posterior (dorsal) horn do?
Receive sensory impulses
What does the anterior (ventral) horn do?
Sends out motor impulses
How is information processed up and down the spinal cord?
- Information enters the dorsal horn
- It synapses with interneurons and travels up a sensory tract to the thalamus
- Thalamus processes the information and sends it to the sensory cortex
- Sensory cortex sends motor information down the corticospinal tract where it synapses at the level it exits the spinal column
- The information then comes out of the ventral horn
What are the spinal cord tracts called?
Dorsal columns
Spinothalamic tract
Corticospinal tract
Which spinal cord tracts are ascending?
Dorsal columns
Spinothalamic tract
Which spinal cord tract is descending?
Corticospinal tract
What information does the dorsal column receive?
Light touch
Vibration
Proprioception
What information does the spinothalamic tract receive?
Pain
Temperature
What information does the corticospinal tract send out?
Motor impulses for voluntary movements
What is a reflex arc?
A fast, automatic and unplanned sequence of actions that occurs in response to a stimulus
What is the spinal reflex?
Integration of a reflex that happens only in the spine
What does a reflex arc consist of?
- Sensory receptor
- Sensory neuron
- Interneuron
- Motor neuron
- Effector organ
What are extensions of the spinal cord called?
Spinal nerves
Where do spinal nerves exit the vertebral column?
Through holes in the vertebra called vertebral foramina
Where is the subarachnoid space ?
Between the arachnoid mater and pia mater
Where is the subdural space ?
Between the dura mater and arachnoid mater
What are the choroid plexi ?
A network of blood vessels covered by a layer of ependymal cells.
They are responsible for producing cerebrospinal fluid (CSF)
What nutrients are circulated by the CSF ?
Oxygen
Glucose
Ions (for nerve signalling/depolarisation)
Which part of the nervous system does the hypothalumus control?
The ANS
Major regulator of visceral activities
What is the key role of the hypothalamus?
Hormone regulation and maintenance of homeostasis
Which part of the brain controls body temperature ?
Hypothalamus
Which part of the brain regulates eating and drinking ?
Hypothalamus
Regulates appetite and satiety
What is ataxia?
Lack of voluntary muscle coordination
Unsteady movements
Difficulties with balance and coordination
Often caused by damage to the cerebellum
Why is cardiovascular health important for brain health ?
The brain requires a constant supply as it has a limited ability to store oxygen or glucose
Rule for cranial nerve locations
2,2,4,4
* 2 - Cerebrum
* 2 - Midbrain
* 4 - Pons
* 4 - Medulla oblongata
Why is the optic nerve useful to assess intracranial lesions ?
The optic nerve spans through the majority of the cranium.
Any abnormal pressure in the brain would likely press on this nerve
Is the vagus nerve sensory or motor ?
Both
90% afferent nerve fibres (sensory) but motor signals are delivered to GIT, cardiovascular and respiratory system
What is (vaso-vagal) syncope ?
Fainting
When the vagus nerve is overstimulated and blood pressure quickly drops
Where are epidurals given and why ?
Verbal, not on slide
Below the level of the midlumbar spine
To ensure the needle doesn’t go directly into the spinal cord
What would damage to any of the spinal tracts lead to ?
Loss of that tract’s function below that level in the body
Nervous System & homeostasis
Whole body
Works closely with the endocrine system to regulate most body functions
Nervous System & homeostasis
Integumentary system
Controls sweating and arrector pili.
Nervous System & homeostasis
Skeletal system
Pain receptors in bone tissue warn of trauma or damage.
Nervous System & homeostasis
Muscular system
- Motor neurons stimulate muscular contractions.
- The cerebellum co-ordinates skilled movements.
Nervous System & homeostasis
Cardiovascular system
Medulla oblongata is the home of the CV control centre. It
governs cardiac output and regulates blood pressure
Nervous System & homeostasis
Endocrine system
- Hypothalamus regulates the pituitary gland.
- ANS regulates hormones (e.g. adrenaline).
Nervous System & homeostasis
Respiratory system
- Respiratory areas in the brain stem control breathing rate and depth.
- ANS regulates airway diameter.
Nervous System & homeostasis
Digestive system
- ANS and enteric nervous system regulate digestion.
- PNS stimulates digestive processes.
Nervous System & homeostasis
Urinary system
- The ANS regulates blood flow to the kidneys.
- The CNS governs emptying of the urinary bladder.
Nervous System & homeostasis
Reproductive system
- Hypothalamus and limbic system govern sexual behaviour.
- The ANS governs erection and ejaculation.
- Hypothalamus regulates the release of pituitary hormones which influence the gonads.
- Nerve impulses elicited by suckling cause the release of oxytocin and milk ejection in nursing mothers.
Nervous System & homeostasis
Lymphatic and immune system
Certain neurotransmitters help regulate immune response